isis: fix processing of outdated LSPs

When receiving an LSP that is older than the one stored in the
database, we should send back the database's LSP instead of the
received LSP.

This is a really serious bug that could cause major issues in the
right conditions.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

holo-isis/src/events.rs

@@ -676,9 +676,11 @@ pub(crate) fn process_pdu_lsp(
             }
         }
         Some(Ordering::Greater) => {
+            let lse = lse.unwrap();
+
             // Update LSP flooding flags for the incoming interface.
             let lsp_id = lsp.lsp_id;
-            iface.srm_list_add(instance, level, lsp);
+            iface.srm_list_add(instance, level, lse.data.clone());
             iface.ssn_list_del(level, &lsp_id);
         }
     }